In 2010 in Australia, there were 0.1 gun murders per 100,000 people, according to the United Nations Office on Drugs and Crime, less than half the rate of a decade earlier. In the United States the murder rate was more than 30 times higher, at 3.2 per 100,000.
The connection looks simple — countries with tighter gun laws and fewer guns have lower levels of gun crime.
But experts say it is not quite so straightforward.
"The irony in the U.K. is that in the four years from 1998 when handguns were fully banned, gun crime continued to rise," said Peter Squires, a professor of criminology at the University of Brighton. "We were in a phase in the 1990s when street gangs were becoming the new urban disorder ... and we were hit by a whole new problem of converted and replica and reactivated guns."
In the long run Squire thinks the change in law did make a difference. Gun crime in Britain has been falling since its peak in 2002 — a decline also seen in other Western countries — and there are now only a few dozen firearms homicides each year.
But, he said, "for the first four years it played into the classic NRA script that gun control has failed."
The U.S. gun lobby sometimes cites peaceful, alpine Switzerland as an example of a country that has many privately owned guns and little violent crime.
Like the United States, it has a strong gun culture and with plentiful shooting clubs — but also a mass citizen militia. Members of the part-time militia, in which most men serve, are allowed to keep their weapons at home, and the country of less than 8 million people owns at least 2.3 million weapons, many stashed under beds and in cupboards.
But while Swiss homes contain guns, but little ammunition, which is largely kept under lock and key at local military depots. Most adult gun users have military training.
And Switzerland went through its own soul-searching after a man named Friedrich Leibacher went on the rampage in the regional parliament in the wealthy northern Swiss city of Zug in September 2001. He killed 14 people and himself, apparently over a grudge against a local official.
The massacre, along with a campaign to reduce Switzerland's high level of gun suicide, led to a referendum last year. It proposed that military-issued firearms must be locked in secure army depots and would have banned the sale of fully automatic weapons and pump-action rifles.
Voters decisively rejected it.
Those who believe tighter gun laws are necessary acknowledge they are no panacea. Norway has strict gun controls, but Anders Behring Breivik shot 69 people dead in July 2011 with a pistol and a rifle he acquired legally by joining a shooting club and taking a hunting course.
But gun control advocates say the alternative is worse.
"There is no act of Parliament, no act of Congress, that can guarantee there'll never be a massacre," former British Cabinet minister Jack Straw, who as home secretary brought in the country's handgun ban in 1997, said Sunday. "However, the more you tighten the law, the more you reduce the risk."
Lawless reported from London. Associated Press Writers Rod McGuirk in Canberra, Australia, John Heilprin in Geneva, Karl Ritter in Stockholm and Matti Huuhtanen in Helsinki contributed to this report.
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